Image analyzing tube



May 4, 1948. M;

cAwElN 2,440,736

IMAGE ANALYZING TUBE Original Filed June 5, 1943 IN VEN TOR.

MADISON CAWEIN ATTORNEY Patented May 4, 1948 MAGE ANALYzING TUBE Madison .Cawem Fort Wayne, Ind., assignor, `by

mesne assignments, to Farnsworth Research Y Corporation, a corporation of Indiana original application June s, 1943,\seria1 No.

This invention relates generally v toelectrooptical apparatus and more particularly to` electronic television imagetubes.` V This application is a division of a co-pending appli-cationof, Madison Cawein, Serial No. 489,869, led June 5, 1943. g,

According to conventional practice, numerous optical arrangements have been employed heretofore for increasing the photo efficiency of electronic television'image analyzing and image -re-` producing tubes.v As is well knownfeach type of image tube functions' to` translate energy from one form to another. `For this purpose each of these tubes utilizes an energy translating element. In an image analyzing tube of the dissector type the energy translating element is a photoelectric 1 energy is translated into electronic energy. In an image reproducing 'tubethe energy translating element is a fluorescent screen, whereby theelectronic energy which impinges thereon is translated into light energy. I

In television image tubes, whetherl they be A"l analyzers or reproducers, it is desired to utilize the available light as eflicientlyas possible. For the present consideration image analyzing tubes, of which a, charge storage tube-is taken as an example, will be spoken of specifically, but it will be understood that the .statements made herein will be equally applicable to other types of image analyzing tubes and to image reproducing tubes as well, for the reason that the optical problems are substantially similar. The only difference is that, in the case of the analyzing tube, the problem is to project the maximum quantity of light reiiected from the subject upon the photoelectric cathode or mosaic, while, in1 a reproducing tube, the problem is to project the `maximum quantity of light emitted by the fluorescent screen onto the viewmg screen.

For maximum photoelciency the optical system employed with a television image tube must have the optimum light gathering property compatible with the limitations imposed by the characteristics of the tube. The light gathering property of an optical system, such as a lens, is directly proportional to the square of the diameter of the lens aperture and is inversely proportional to the square of the distance which the light must travel from the lens to the focal plane. Thus, in a given interval of time, the ratioof the focal length of a lens to the diameter of the lens aperture is a measure of the light which may be prg 551er example, an f/ 1.5 lens. Since the quantityv Divided and this 16, 1947, Serial No. 769,006

j 6 claims. (o1. 25o-'5153),'

ich

application August jected upona charge storage tube photoelectrlc electrode located in thefocal plane of the lens. Therefore, it follows that, in a given interval of time, the smaller this ratio can bemade the greater will be the light which is incident upon the photoelectrlc electrode to form the opticalimage. 'I'his ratio is commonly known as the f/ number of the lens and designates the rapidity or speed thereof, the lower f/ numbers being applied to the faster lenses. l

`With tubes having opaque energy translating elements, the optical systems which have been utilized heretofore haveconsisted of a lens-or a system of lenses, necessarily disposed externally of the tubes `by reason of the requirement that the scanning apparatus have unobstructed vaccessto the sensitized surfacelofthe energy translating element. Consequently, the aperture and focal length of such a lens are limited by the physical dimensions of the tube. The tube dimensions are determinedprimarily by considerations such as the focusing and scanning arrangements required for the operation of the tube. i Hence, it is seen that the minimum f/ number of the optical system is fixed by the tube dimensions. For example, in a charge storage tube, the fastest practical lens which may be used successfully is an f/2.5 lens.

In the operation of television image tubes the time during which an optical image is projected onto the energy translating element is determined by the frame scanning frequency. By reason of this limitation, only a relatively small quantity of light may be projected upon the photoelectric electrode of a charge storage tube to :form the loptical image thereon, when prior art optical arrangements are used. Since the exposure time of the electrode is limited by the frame scanning frequency, the only possible way of projecting more light upon the ,electrode is by utilizing an optical system having =a speed greater than f/2.5. As previously indicated, such an expedient is prohibited where the optical system consists of a lens disposedlexteriorly of Vatube having an opaque electrode. Y

There remains, however, the alternative of disposing the optical system adjacent the end of the tube in which the energy translating element is located., By this means it is possible to shorten the focal length of the lens sufliciently so that it may be placed in such relative proximity to the `photoelectric electrode that the distance required for the light to travel from the lens to the electrode is shortened materially. Such an arrangementpermits the use of a much faster lens, say,

of light projected onto the electrode va-ries inversely as the square of the f/ number, it is seen that, by the use of an f/1.5 lens, it is possible to project approximately three times as much light onto the photoelectric electrode than is possi-ble with arrfr/Zlens.

There is, however, arlisadvantage'to this-latter type of arrangement in that it requires the use Y of a translucent energy translating element.

This, of course, is required since theirljghteme fling a speed of f/.5 instead of a system having the television subject is projected onto one surface of the electrode, while the-electnonlimage must be formed on the oppositeside-whereby-to permit scanning thereof. It is Well'known that translucent structures of thisgchalaterfalle dim cult to form since they mustzfbc. thirlaenlflgllitO render them semi-transparent and the photoelecztric layer must be of uniform thickness, in order not to introduce distortions. Obviously, a structure meeting these requirements has a low photo 'efliciencsh a-resu-lt the gain infeicieno'wwhich is obtained by,the--*useiofythef'fasteri-lensgsystem is substantiallycounterbaiancedby reason-of the light -floss introducedb57J ther employment-0f `the translucent energy-translating-element f @Irl View ofthe limit-ationsV andedisadvantagesof .the attempts' Whichhavegbeenmade heretofore to; increase the photo f; e'cencyfof -f a-jtelevision image tubebyimeans of optical systems disposed externally of the tube, it is apparentAthati-any arrangement ofT thisj characterf-wil'lenot produce `,an increase; in;l eiiiciency suiciei-,itgordinarily- -to render; thevuse-thereof; otmuch practical value.

1t is; an obj ectof thegpresent invention; therefore; to provide anelect-ro-opt-ical# device in -which there is Yincorlg-iorated'anoptical--systerrmwhereby t0 increase the -photo eflciency-of4 the device.

A`JAnotlierjobject of `the invention-*isf to providea television-'imagejtube incorporatingl -an optical fsystem @having `vr4largelightgathering; properties, flvhereby to increase thephotol efficiency- #of 2 the ube. l

"Another object of the inventionfis to provide anv improved chargestorage -tubesuchas-an iconoscope-liaving' and opachie-rriosaic,J -andincorporating anv ,optical 'systemeof' fa oharactereto-permit orthogonallscanning: of the mosaic.

' ",One"opticarsystem which possesses the char- ;acteristicsrequiredto r*increase-e the photo L effi- ;ciency of a. televisionfimage-v tube utilizing) an ropaque energy translating-elementis theso-called 'Schmidtoptical system- ,#Such-asystem has been employed heretofore Ain-connection withastronomical telescopes and cairieras.- .Brieily,` such a, lsystem-comprises aspherical-reflector, oppositet'o which there isidisposed-in spacedfrelation, .at lens `havinga coni-lguratiori^ suitable to correctlforthe spherical aberrationofv the treflector.- ,Approximatelymi'dway-between the relectorand-.the oorrectingrlens irithe focal plane ofi theffreector, there is jioated Aaspherical-memberhaving' fits surface disposedparalleltoflthei-surfacel-of'the "reector, Inlthe casey wherethe systeml-is-employed in a telescope, the surface ofthefiocal es plane member is theyscreen upon Vwhichfthei-irnage is; projectedand'from -which it may befviewed.

vIn the casewhere-the lsystem isused'with: a camera, a ip,hotzpgraphicii-1m isdisposed 4in .the A,focal quently; it-maybeused-advantageouslyifon applications-requiring a wide-anglecoverage together withY an extremelysmallf/wnumber.A For; example, aSchmidtopticalN systemhaving-afspeedxof -fas aSp6df;of f/2.5, the light' which is incident upon the photoelectrie electrode of a charge storage tubezisa-.timesegreater in the former case than it is"finftheiglatten-case.

accordance with the present invention, there isgplieyidedeangeuacuated envelope having a body portionqandagstem portion affixed thereto. Ad-

janentztoth'egwallvof the body portion connecting with thehstem portion, and Within the envelope, there is provided an Minwardly' facing concave spherical reecting sur-face. Preferably, thisv surfacef-may-beformed-on theinside Aof` afspherically shaped envelope 'wall.- liii-nl'aperture 4is formed in thissurf'ace topermitcommunication betweenfthe body and-1ther-steinportionsr .oftV thetube. 'The Awall of-the# bodylportiony opposite 1to1 the wall adjacent-v tothefreiiecting surface, lisi. transparent and-may loeginJ thei formof-Y a lens: which has a-con-fig-uration-` `suitable to-correct for the sphericalf .aberrations-ofi the-reflecting surface. The icorrecti-ng--lens-lallternatively may beelocated VeX- ternal-ly of the-envelopeladiaeent -the transparent iwalll." lGllhere'f-ialsois provided, within the envelpefan energytranslating element-having a con- 'vex" spherical photoelectric-surface, `which .is arrangedparallel to the-reflecting. surface. The energytranslating-elementi-ot the tubev is l located between the correcting lensn and v the reflecting surfacein-thebodyportiorr of the-tube. This ele- -ment hasafesurfaoefareaf'whichV is. small relative "to, the surface areaof-thelreecting surface. The energyfit-ranslating element is.disposed= in alignmentwiththeeaperture formed ini thereiiecting surface. I i v There is mounted in thev-ls'ternf portionfof-` the tv-bef electron-iok apparatusfor-cooperative :opera- -tign-=-w ith the energy; translating-element. f Also, there -is-disposed'adjacent to the. stem vportion of the tube-envelope,-'suitablaapparatus for effecting 'focusing and-=-sc a nning, -.whereby-- to enable Vthe electronic -apparatustof perform--its function. --Aiso, suitable electrical @connections ...are made through l'thee tube f envelope-Ito the Y apparatus -mountedherein- 4 n 1 accordance `with4 a= speci-lic embodiment vrof the-inventionithe energyI translating element is a mosaic surface.` Theelectronc means mounted iii-ethe-l stemv-porti'on--of'- theftubey envelope 4is `an velectrongun.' l Y "MJT-he focusingand scanning apparatus-i utilized iny-eonnectionvwith atelevisionimagetube in accordancelwi-th=the kinstanty invention, may be electromagnetic and/or electrostatic, :as '-desireol. I :For-afbetter understanding, of this. invention together--'With other-andsf-urther objects; thereof, reference; -is-i had Vto2 the following description 4taken-.in -,-eor-mection.V with the. A.accompanying drawing and-its sc opefivvill` :bepointed .out in: the appendedclaims.v Y y -iIn the accompanying-drawing, the single '-gure isaAv sectionaliviewitof .aniy iconoscopeor: orthicon imageLanalyzingtubeembodying.l the 1 invention.

Referring ynowa to= theldrawing, therey is` illustrated. .an ficonoscopeltor: orthicon type.- ofcharge storage.. tubehaving .a fglassaenvelope. l; surround- Yin-ggthe mainonbodyeponton'.- of: the tubez; and; a

stem portion envelope 2. The `space enclosed by the envelopes is evacuated. One end wall 3 of the body portion ofthe tube is spherically shaped so that a concave surface is formed facing inwardly of the tube. The wall 3 is provided witha centrally disposed aperture, whereby to provide .communication between thebody and stem portions of the tube. The opposite end wall is formedby a transparent lens `II, the outer surface of which Ais flat and the innersurface of which has a configuration suitable to correct for spherical aberration.` The center of curvature for the wall 3 is located approximately at the center ofthe lens `ll.

A layer of light-reflecting material is deposited on theconcave spherical surface of the envelope wall 3. Preferably, 4 this material is gold so that the surface formed is a good reflector of invisible light rays, such -as the infrared rays. However, other materials such as silver may be employed with substantially equal facility within the scope of the invention. The reflecting surface 5 is deposited on the glass wall by sputtering or any other suitable process An electri-cal connection 6 is made to the refleeting surface 5 and may be extended through the tube envelope I as shown.l or in any other well known manner.

In the main body portion of the envelope I a spider-like supporting structure may be einployed for the photoelectric electrode. As illustrated herein, this structure comprises a plurality of small stiff wire members such as 1 and 8, the

` outer ends of which may be inserted in suitable recesses formed in the walls of the envelope I. The ends of the supporting members 1 and 8 may be anchored in the envelope `by fusing, cementing, or other suitable means. It is to be Electrical connections to the electrodes mounted in the stem portion of the tube are made through the press portion of the stem, as shown.

Referringnow to the operation of the embodiment of the invention illustrated, it will be assumed that light which is reflected from a subject is directed through the lens plate 4 from the left, as viewed in this ligure. This light,

. when reflected from the spherical surface 5,

noted that this specific structure and the specil fied means of attaching it to the tube envelope are merely illustrative, since it is considered to be obviously withinthe scope of the invention to provide an equivalent structu-re of this or other form which may be anchored in any other well known manner.

Each of the supporting members 'I and 8 is angularly formed at the inner end thereof and serves to support the energy translating element. This element may be formed by attaching a suitable metallic backing plate 9 in any Well known manner to the inner ends of the supporting members 8. The configuration of the backing plate is convex on the side thereof facingr the reflecting surface 5 and is lparallel thereto. A mosaic surface I I may -be applied to the spherically convex surface of the backing plate 9 by evaporation or other conventional process. A conductor I2 may be attached to the backing plate 9 as shown and passed to the outside of the tube through a suitable seal formed inthe central portion of the correcting lens 4.

A conventional electron gun, electrostatic focusing apparatus, and electrostatic deflecting systems are mounted in the stem portion envelope 2. The electron gun comprises a thermionic cathode electron emitter I3 which is heated by a filament |14. The gun also includes a grid like structure I5 and a first anode I6, the latter of which is arranged for cooperative operation with a second anode I'I, which is in the form of a wall coating on the tube envelope. The anode structure is for the usual purpose of focusing the electron beam. The deflecting system comprises a pair of horizontal deflecting plates I8 and a pair of vertical defiecting plates I9.

forms an optical image on the mosaic surface II whereby the lightenergy is translated into electronic energy and creates an electrostatic charge image on the mosaic surface. In the case that such a tube is used as an iconoscope, a high velocity electron beam is caused to scan the mosaic surface under the control of the illustrated scanning apparatus. The television. video signals thereby generated are applied to conventional amplifying apparatus (not shown) by means of the conductor I2 connected to the backing plate 9. In the case where the tube is to be employed as an orthicon, the mosaic surface II is scanned by a relatively low velocity electron beam in a well known manner effected by suitable modification of the deiiecting system and the voltages applied thereto,

To those skilled in the art, itwill be apparent that an image tube according to this invention possesses l numerous advantages," irrespective of the type of tube.` In all types of tubes the photo efficiencies thereof are increased to a marked degree. Also, tubes embodying the invention permit the use of solid or opaque energy translating elements with all of their inherent advantages.

In an iconos-cope `or orthicon, it obviates the necessity of angular scanning. The mosaic may be scanned orthogonally and thus there is eliminated the heretofore employed arrangements for making a correction for the so-called keystone or perspective distortion.

The photo efciency of a television image tube, or other device embodying the invention, not only is increased by the described arrangement, but also is maintained constant by reason of the factthat the concave light-reflecting member is .sealed within an evacuated envelope. Thus, the reflecting surface is not'subject to deterioration from such causes as dust, for example. i

It should be noted that it is immaterial whether the outer, inner or both surfaces of the correcting lens be curved, so long as this member suitably compensates for the aberration of the reflecting member, whereby an undistorted image is formed.

While there has been described what, at present is considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and therefore, it is aimed in the appended claims to cover all such changes and modifications as fall Within the true spirit and scop'e of the invention.

What is claimed is:

l. An electroeoptical device comprising, an envelope having two oppositely disposed walls, a concave light-reflecting member within said envelope adjacent one of said walls and facing the other of said walls, a light-refracting member' spaced relationship to said reflecting member and facing-fia;electronic.ineens-- for producing. ay

cathode? rayy withinsfsaidfienvelope. disposed. incooperative relationship -to said photosensitive niemben .andsmeansvdisposed :to produce. within sain :envielope an. electron-f deecting fieldY having an? :intensity v1amitieeperiodicallyl according .to a.

predetermined :scanning pattern.

Y 22A te vision iconoscopre comprisin'g.an ening4 auxtransparentf WalL,y a; concave lecti-ng member in said;` envelope-facing;

facingsaifdreiilectingzmember, .au convex l.mosaic d envelopewv isposed in`4 spacedparallel vre- A to sardi. reflectingv r member, and; an e.-e ron -guz1i envelope;'disposed` in cooperative relationship :to: said. mosaic.

A'teie on.`4 icono'sc'ope.comprising; an enpeha L., a transparent' wall;r aspherical li'g terecctinamember vin said envelope facing sa-id Atranspaiu'e tl Wall,V a` lens to correct for, ca aberration of said-1reflecting` member a said transparent)- W'all; and having:v the erica! surfacethereof .1 parallel ta-and facing the stem portion of said envelope, an electron gun mounted; in Vsai-d stemportion, and electro# static focusing and' scanning/,meansdisposedfad# jacentgto-said electron gun.

5. A televisionk iconoscopeI comprising; ane envelope having a body portionzand a sternL portion, said. body portion having-two'v oppositelyc-disposed walls, an inwardly facingspheri'callight'- reecting member formed-in one ,of saidlvvajlls; a

lens to correct foixspherical ,aberrationof' said reilecting 7 member formed in the other of 1' s aid 6. A .television` chargestorage iinagefanalyzing tube comprising; an envelopahaving a .transparent wall, .a concavedightfreecting. member in said envelope vfacing said.Y transparent `a lightvrefracting member .to correct. for aberration produced by said reflectingmember disposed. in 'spaced relation to.. saidreecting. melober;i a mosaic electroder` in said .t envelope., disposed. vin spaced .relationship to .and` facing saidreflectng member; an electron Agu-n fin said envelopesdisposed Ycooperative relationship `.tozfsaidV ,mosaic electrode rforV directing a.. cathode. ray. onto.,said mosaicA electrode,` and.` means for deilecting .said cathode ray.y over said mosaic electrode?.tov generate video signals representative.: of an.A optical image projected 1 onto saidmosaic electrode-by means off-said reecti-ng member. Y

MADISON. CAWEIN... 

